The invention relates to a rotor for a reluctance machine comprising a cylindrical soft-magnetic element, wherein the soft-magnetic element has cutouts for forming magnetic flux barriers and at least some of the cutouts are filled with an electrically conductive and magnetically non-conductive filler material, in order to form a starting cage of the rotor.
Rotors for synchronous reluctance machines are usually equipped with a cylindrical soft-magnetic element which is arranged coaxially on the rotor axis. In order to form at least one pole pair or gap pair, the soft-magnetic element comprises flux-conducting and flux-blocking portions, which differ from one another by a magnetic permeability of differing degrees. The portion with high magnetic conductivity is identified, as is known, as the d-axis of the rotor, and the portion with comparatively lower conductivity is identified as the q-axis of the rotor. An optimal degree of efficacy of the reluctance motor and therefore an optimal torque yield is provided when the d-axis has the greatest possible magnetic conductivity and the q-axis has the lowest possible magnetic conductivity.
This precondition is often satisfied by the formation of a plurality of cutouts, which are filled with air, in the soft-magnetic element along the q-axis, as a result of which the magnetic conductivity decreases and consequently the magnetic flux in the direction of the q-axis is inhibited. The soft-magnetic element constructed in this way is then mounted on a rotor shaft and fixed axially and also tangentially.
For stability reasons, one or more flux barriers is/are divided into two by radially oriented inner webs. The web arrangement increases the strength of the laminated core, which in particular optimizes the rotor stability during operation. The width of the webs is low in order to keep the magnetic permeability in the q-axis as low as possible. Webs, which delimit the flux barriers from the rotor periphery, also run on the outer rotor periphery.
Synchronous reluctance motors are generally fed via a frequency converter, as a result of which the rotation speed can rise from 0 to operating speed and can be adjusted during operation. In particular, the rotation speed for starting the motor can be increased in steps. If the synchronous reluctance motor by contrast is operated in a fixed grid, the use of a starting cage is necessary in order enable asynchronous starting. As soon as the rotation speed of the rotor approaches the synchronous rotation speed, the reluctance torque becomes predominant and the rotor runs synchronously with the magnetic rotating field. However, the structure and manufacture of conventional starting cages, comprising conductor bars and short-circuiting rings, have been comparatively complicated and expensive to date.
The object of the present invention is to develop a rotor for a reluctance machine in such a way that said rotor can be used within a line-start synchronous reluctance machine in a fixed grid.
According to the invention, the rotor of the generic type is developed in such a way that the ratio between the area of the filled regions of the flux barriers and the area of the non-filled regions of the flux barriers for at least one rotor pole, preferably for all of the rotor poles, is at least 0.2.
The area of the filled region of the flux barriers is the filled area which is given by sectioning transverse to the axial axis of the rotor, that is to say the cross-sectional area of the magnetically non-conductive and electrically conductive filler material used. In particular, said area is sum of the area of the filler material for all of the flux barriers of the rotor.
The area of the non-filled flux barriers is given in an analogous manner by the region of the flux barriers which are filled with another filler material or are not filled, for example contain air.
The rotor itself can be designed, for example, as a laminated core, wherein the individual laminate sections are distinguished by the area ratio according to the invention.
In order to form the starting cage, the flux barriers or partial regions of the flux barriers of a radially outer rotor region are filled with the electrically conductive filler material. The inner rotor region which is delimited therefrom comprises the unfilled flux barriers or flux barriers which are provided with the other filler. Ideally, the result is an annular outer rotor region. A critical factor in determining the operating characteristics of the rotor is the ratio of the filled flux barrier area to the non-filled flux barrier area. Investigations have shown that reliable synchronization of the rotor with the frequency of the grid voltage can take place starting from a ratio of at least 0.2.
Aluminum or an aluminum alloy preferably serves as filler material. Materials of this kind can be introduced by casting processes or pressed in by die-casting processes. As an alternative or in addition, it is likewise conceivable to introduce filler materials of this kind into the corresponding cutouts in the rotor geometry already in the form of solid bodies.
The remaining flux barriers, that is to say those which are not filled with a corresponding filler material, can be filled, for example, with a different filler material, for example by a paramagnetic material for reducing the permeability.
In a particularly preferred refinement of the invention, the ratio is in a range of between 0.2 and 3, preferably in a range of between 0.3 and 3, and ideally in a range of between 0.75 and 1.5.
For determining the ratio according to the invention or the advantageous ratio, it may be expedient for only those flux barriers which are at least partially filled with corresponding filler material to be taken into account for calculating the ratio. Furthermore, it is also possible for only those flux barriers of which the ends reach the rotor periphery or come close to said rotor periphery to be included when calculating the ratio. This configuration of the flux barriers is disclosed, for example, by the known “Vagati design”, in particular by U.S. Pat. No. 5,818,140, reference being made to said document in its entirety here. In the case of rotor geometries of this kind, both ends of the flux barriers reach the rotor periphery, that is to say the flux barriers are characterized by a banana-shaped design. These flux barriers have a critical influence on the reluctance behavior during rotor operation, and therefore it may be expedient, under certain circumstances, to take into account only flux barriers of this kind for calculating the ratio.
According to a particularly preferred refinement of the invention, it may be advantageous when the ratio between the filled and the non-filled region of the flux barrier which is situated on the inside in the radial direction of the rotor has a value of at least 0.2. This ratio can apply for at least one rotor pole, preferably for all of the flux barrier portions. In a further advantageous refinement, the ratio of the flux barrier which is situated on the inside in the radial direction of the rotor is in the range of between 0.2 and 2, particularly preferably in the range of between 0.35 and 0.8, ideally between 0.35 and 0.6.
Furthermore, it is conceivable that the area of the filled region of the flux barrier which is situated on the inside in the radial direction, which area results on account of the above ratio specification, serves as a measure for the areas of the filled regions of the flux barriers which are situated further on the outside. This means that the area of the filled region at least of one further flux barrier of a rotor pole, which further flux barrier is not the inner flux barrier, corresponds to the area of the filled region of the inner flux barrier or is virtually identical to said area. Under certain circumstances, this precondition cannot be met for the flux barriers with the smallest area since said flux barriers do not provide enough filling space for the area specification. In this case, the area specification applies at least for the partially filled flux barriers.
The invention further relates to a reluctance machine, in particular a synchronous reluctance machine, comprising at least one rotor according to the present invention or an advantageous refinement of the present invention. The properties of the reluctance machine obviously correspond to those of the rotor, and therefore are not described again here.
The machine preferably serves for driving the pump. The invention therefore also includes a pump comprising a reluctance or synchronous reluctance motor according to the present invention.
Owing to the rotor geometry according to the invention and the corresponding filling ratio of the individual flux barriers, it is possible to produce an optimum starting cage, but with the mass of the filler material and therefore the mass of the starting cage formed being kept as small as possible. A line-start synchronous reluctance motor can be formed by the rotor, it being possible to operate said line-start synchronous reluctance motor in a fixed grid without problems and also to start said line-start synchronous reluctance motor without a frequency converter owing to the design of the aluminum cage, and said line-start synchronous reluctance motor running until complete synchronization with the grid voltage.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.